The present invention relates to a single-lens reflex electronic image pickup apparatus and, more particularly, to an improvement in mechanism of an optical system of an electronic image pickup apparatus.
A generally-used single-lens reflex electronic image pickup apparatus in which a subject image formed through a lens is directly observed by an optical finder, has the following features. The apparatus causes no parallax and consumes little power as compared with an apparatus having an LCD finder. The electronic image pickup apparatus can be constituted chiefly of an image pickup unit and a finder unit.
The image pickup unit includes a lens unit for forming a subject image, a beam splitter for splitting a light beam, and an image pickup element for converting a formed optical image into an electric signal.
The finder unit is provided on one of plural light emitting surfaces of the beam splitter, and optical parts of an optical finder are arranged along the optical axis. The beam splitter has a 45xc2x0 reflection surface, and its through-beam is guided to the image pickup element and its reflected beam is guided to the finder unit.
Jpn. Pat. Appln. KOKAI Publication No. 6-160942 discloses an optical finder which has been known conventionally. The optical finder includes a reflector for reflecting light incident through an image pickup unit of a camera and a reticle plate having a field frame pattern. The inclination angle of the reflector to the optical axis of the incident light can be adjusted, and the reflector can be swung with respect to an axis parallel to the optical axis. The reticle plate is supported such that it can be rotated about the optical axis.
In the above optical finder, the position of a subject image is adjusted up or down by adjusting the inclination angle of the reflector. Since the reflector is swung with respect to the axis, the subject image is moved right or left. If the reticle plate is rotated, the relative position of the subject image and field frame is adjusted.
The foregoing conventional electronic image pickup apparatus has the following problem. Since the size of an image pickup element such as a CCD is much smaller than that of a silver-salt film, high precision is required for the mechanism of the image pickup unit, especially a single lens, a lens mirror frame and a lens moving mechanism of the lens unit. Since, in particular, a single-lens reflex electronic image pickup apparatus is a high-grade one, it requires high optical performance, with the result that the time for adjusting and inspecting the lens unit is considerably longer than that for doing the finder unit.
To resolve the above problem, the lens unit having a number of parts to be adjusted and inspected can be combined with both a beam splitter and an image pickup element, which need not be adjusted in particular, into a single unit. However, this throws a product line out of balance and requires an extra attention to prevent the lens unit from being damaged when it is disassembled or reassembled. Furthermore, most of electronic cameras are not adaptable to the combination of the beam splitter and image pickup element because they are assembled by selectively combining a plurality of lenses and a plurality of image pickup elements having different numbers of pixels.
Since the conventional electronic image pickup apparatus is so constituted that a through-beam of the beam splitter is guided to the image pickup element, the image pickup element is arranged behind the beam splitter, thereby increasing the dimensions of the apparatus in its front-to-back direction. In particular, a camera having a plurality of circuit boards stacked at its front and back, such as an electronic camera, is increased more greatly in dimensions in the front-to-back direction.
The balance between through-light and reflected light of the beam splitter is varied according to whether a beam incident upon the beam splitter is polarized or not. If, therefore, the polarized beam is present in a portion of a subject, a difference in luminance between the light incident on the image pickup element and that incident on the finder is caused in the portion of the subject. The degree of influence of such a polarized beam is proportionate to the incident angle or the reflection angle on the reflection surface of the beam splitter. Consequently, it is desirable that the incident angle or reflection angle be smaller than 45xc2x0.
An object of the present invention is to provide an electronic image pickup apparatus in which a beam splitter and an image pickup element are incorporated into an optical finder unit together with optical parts used for an optical finder to protect the beam splitter and image pickup element, which are expensive, even when a lens system is troubled, and the image pickup element is detached from the lens system and replaced with another as required to quickly respond to a model change.
Another object of the present invention is to provide an electronic image pickup apparatus in which a beam splitter and an image pickup element are combined into a small unit to improve the precision of collimation between the emitting surface of the beam splitter and the image pickup element and to facilitate the management and assembly of the beam splitter and image pickup element when the apparatus is produced.
Still another object of the present invention is to provide an electronic image pickup apparatus in which an image pickup surface of an image pickup element is inclined to the light beam incident upon a beam splitter to decrease the dimensions of a lens system in its optical axis direction and thus decrease the dimensions of the apparatus in its front-to-back direction.
To attain the above objects, the electronic image pickup apparatus of the present invention has the following characteristic constitution. The other characteristic constitution will be clarified later in the description of the embodiment.
According to the present invention, there is provided an electronic image pickup apparatus in which a light beam of a subject image penetrating an image pickup lens is split into light beams by a beam splitter, one of the light beams is converted into an electrical signal by an image pickup element and then recorded, and other light beam is observed by an optical finder, wherein the beam splitter and the image pickup element are incorporated in an optical finder unit together with optical parts used for the optical finder.